Dual balanced reciprocal waveguide phase shifter

ABSTRACT

A phase shifter for balanced dual waveguide systems is disclosed for high power broad frequency range applications. An increment in electrical length is provided which is reciprocal for any dual balanced network including TR and ATR electron discharge devices or nonreciprocal differential ferrite phase shifters utilized as isolators or circulators. A dual waveguide structure is provided in one section with dielectric loading means to reduce the guide wavelength and increase the phase length while the abutting waveguide section is provided with means for reduction of the waveguide width to increase guide wavelength and decrease phase length. The first means comprises a member of a dielectric material such as aluminum oxide and the second means comprises a conductive plate member. The desired performance characteristics with the addition of the balanced reciprocal phase shifter means are attained over, illustratively, a relatively broad frequency band of approximately 40 percent. Balanced systems including short slot hybrid and magic T hybrids, as well as directional couplers together with nonreciprocal differential phase shifters or dual gas switching tubes are readily provided with any desired degree of additional reciprocal phase shift. In an illustrative embodiment the incremental reciprocal phase shift means is provided within a differential ferrite phase shifter without disturbing the overall mechanical symmetry of the system packaging.

United States Patent 11 1 Booth Sept. 3, 1974 22 Filed:

[ DUAL BALANCED RECIPROCAL WAVEGUIDE PHASE SHIFTER Alfred E. Booth, Marlboro, Mass.

[73] Assignee: Raytheon Company, Lexington,

Mass.

Mar. 1, 1973 [21] Appl. No.: 337,255

[75] Inventor:

OTHER PUBLICATIONS Bacon et al., Some Applications of the Principle of Variation of Wavelengths in Wave Guides by the Internal Movement of Dielectric Sections, IEE, Vol. 93, pt. III A, pp. 633-638.

Primary ExaminerJames W. Lawrence Assistant Examiner-Wm. I-I. Punter Attorney, Agent, or Firm-Edgar O. Rost; Joseph D. Pannone; Harold A. Murphy 57 ABSTRACT A phase shifter for balanced dual waveguide systems is disclosed for high power broad frequency range applications. An increment in electrical length is provided which is reciprocal for any dual balanced network including TR and ATR electron discharge devices or nonreciprocal differential ferrite phase shifters utilized as isolators or circulators. A dual waveguide structure is provided in one section with dielectric loading means to reduce the guide wavelength and increase the phase length while the abutting waveguide section is provided with means for reduction of the waveguide width to increase guide wavelength and decrease phase length. The first means comprises a member of a dielectric material such as aluminum oxide and the second means comprises a conductive plate member. The desired performance characteristics with the addition of the balanced reciprocal phase shifter means are attained over, illustratively, a relatively broad frequency band of approximately 40 percent. Balanced systems including short slot hybrid and magic T hybrids, as well as directional couplers together with nonreciprocal differential phase shifters or dual gas switching tubes are readily provided with any desired degree of additional reciprocal phase shift. In an illustrative embodiment the incremental reciprocal phase shift means is provided within a differential ferrite phase shifter without disturbing the overall mechanical symmetry of the system packaging.

1 Claim, 15 Drawing Figures PATENTEDSEP 3W 3.8%.868

SIEEI 3 0f 4 ANTE NA, l6

20 I m 3db COUPLER F/G 5 2? 30 pR/OR ART /4 D v 26 GAS TR TRANSMITTER RECEIVER /2 DUPLEXER Z8 ANTENNA, I6

RECEIVER 0 2 DUAL /4\ GAS 7 26 o /28 TRANSMITTER 9o REcElvER /2 24 w F/(i 6 T ANTENNA, T6 ADDER RECIPROCAL PHASE SHIFTER 20 I 28 \Tl m 22 RECEIVER DUAL /4 'eAs TR 0 26 TRANSMITTER H 1 F/G. 7 U2 [fig ANTENNA,I6

20 REcElvER 26 /0 2\2 -/8\ /4 gig /22 TRANSMTTTE.

ISOLATION db AIENTEDsEP 3:914

PR/OR ART sntnuuu I F/G 95 i- OPERATING RANGE FOR WR284 WAVEGUIDE l 1 1 l I FREQUENCY (6H2) DUAL BALANCED RECIPROCAL WAVEGUIDE PHASE SI-IIFI'ER BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to waveguide transmission systems, and particularly, to broadband high power reciprocal phase shifters for balanced systems.

2. DESCRIPTION OF THE PRIOR ART Balanced waveguide transmission systems are well known in the art. One type referred to as a balanced duplexer is described in the next Microwave Duplexers, by L. D. Smullin and C. G. Montgomery, Vol. 14, McGraw-Hill Book Co., Inc., New York 1948. A typical embodiment of the balanced duplexer is shown in US. Pat. No. 2,586,993, issued Feb. 26, 1952, to H. J. Riblet and assiged to the assignee of the present invention. Referring now to the drawings, particularly, FIG. 5 a prior art balanced duplexer employing dual TR gas switching devices is diagrammatically illustrated. Dual rectangular waveguide sections and 12 are coupled by a hybrid coupler 14 so that power incident at one end is evenly divided and appears in equal quantities at the terminals of each of the dual waveguides. The input ends of waveguides l0 and 12 are connected respectively, to antenna 16 and transmitter 18. One of the advantages of the balanced duplexer is that it permits transmission and reception by means of a single antenna.

The output ends of waveguides 10 and 12 are connected to dual TR switching devices 20 having plural discharge gaps and microwave permeable windows sealing each end of the dual structure. Keep alive electrodes provide for the ignition of an intense gaseous discharge within each tube. A second pair of dual rectangular waveguides together with a hybrid 26 are connected to the output end of TR devices and are terminated in a receiver 28 and load 30 connected to waveguides 22 and 24.

During reception low level signals are received by antenna 16; are equally divided; do not fire the TR devices 20; and proceed along the waveguides 22 and 24 to be again divided and combined to pass to receiver 28 and a nonreflecting-type load termination 30. Inherently, balanced duplexer systems provide for broadbanding characteristics in addition to the single antenna capability.

Another example of a balanced waveguide system is found in nonreciprocal difierential ferrite phase shifters employing magnetically-biased ferromagnetic bodies disposed within dual waveguides. An example of such phase shifters is found in US. Pat. No. 3,187,274 issued June 1, 1965 to J. Q. Owen et al., and assigned to the assignee of the present invention. Referring again to the drawings in the present application, particularly, FIG. 3A an example of the prior art is illustrated. Differential phase shifters connected in the manner shown provide for a nonreciprocal differential phase shift of two waves at the same frequency interacting with the magnetized bodies within abutting waveguides. In FIG. 3A the energy from the transmitter entering port 1 of a magic T 32 is split and transmitted over waveguides 34 and 36 to phase shifters 38 and 40. The power divided between the two phase shifters permits the handling of very high powers in transmission systems. A coupler 42 interconnects the output of dual phase shifters 38 and 40 with the energy in the proper phase emerging from port 2 terminating in the antenna. Any high power energy reflected from port 2 is absorbed by a high power load connected to port 3. Any reflection from port 3 is absorbed by a low power load connected to port 4. The circulator illustrated in FIG. 3A terminated with loads at ports 3 and 4 functions as an isolator in a microwave transmission system.

In FIG. 3B a dual phase-shift circulator is illustratrated which functions as a duplexer with the direction of the power flow indicated by arrow 44. In a typical application power from the transmitter entering port 1 emerges only from port 2 which is connected to the antenna. Any energy entering port 2 from the antenna emerges only from port 3 which is connected to the receiver. Similarly, any power entering port 3 emerges from port 4 connected to a terminating load. Such an arrangement permits isolation of the transmitter from antenna mismatch and problems. Finally, the ferrite circulator being a passive device has infinite life.

In all of the foregoing illustrated balanced microwave components, particularly, those used for high power operation over relatively broad frequency ranges it is necessary that the adajcent waveguides have specific phase relationships in order for the overall system to function. In the case of the duplexers utilizing TR gas switching tubes essentially a 0 reciprocal phase difference is maintained. In the circulator employing nonreciprocal differential ferrite phase shifters approximately a phase difference is required. The present invention is concerned with the requirement for the addition of reciprocal phase shift increments of any desired value, typically 45, 90 and in balanced microwave systems without substantially disturbing the mechanical symmetry of the dual balanced system.

An example of a known prior art structure for accomplishing the addition of an increment in electrical length is shown in FIG. 9A. The structure is referred to as a folded trombone system 46 consisting of many E-plane 90 bends 48 and 50 connecting dual waveguide sections 52 and 54. The traditional way of obtaining a 90 phase step between pairs of otherwise balanced waveguide sections is to add a physical length of a quarter of a guide wavelength to one side of the assembly. In keeping with the principle of reentrancy of such systems a )tg/8 spacer is added to two legs on one side to result in a longer section 56 relative to the short section 58. In an exemplary assembly involving WR 284 waveguide for the propagation of S-band frequencies a typical trombone system would require the addition of approximately 1.25 inches in length to long section 56 to result in an overall length of 12.25 inches relative to the short section having a total length of 11 inches. It is also inherent that attempts to achieve any increment in the electrical length with the desired electrical characteristics restrict the frequency bandwidth capability.

SUMMARY OF THE INVENTION In accordance with an embodiment of the invention a dual waveguide structure having substantially the same overall length is provided with a first reducedwidth section and a juxtaposed second dielectricloaded section. The balanced configuration provides any degree of reciprocal phase shift desired for a high power broad frequency range applications. The structure is readily adaptable to any balanced microwave systems utilizing short slot and magic-T hybrids and directional couplers. The reduced-width section provides for a decreased phase length while increasing the guide wavelength. In this section operation is above the TE cutoff mode at the lowest desired frequency. In the dielectric-loaded section an increased phase length and reduction in guide wavelength is provided to maintain the balanced symmetry in the overall system while providing the desired reciprocal phase shift. In the dielectricloaded section the only requirement in overall performance is the avoidance of resonances and/or highorder modes in the structure.

The dual waveguide structure in an embodiment of the invention at S-band provided satisfactory phase error and isolation response characteristics over an overall bandwidth of approximately 39 percent. In view of the fact that the embodiment does not employ any inherently lossy elements the balanced reciprocal phase shifter exhibits very low insertion loss. The structure is capable of operation at high peak and average power levels with the elimination of bends etc. of prior art systems. Further, inherently temperature-sensitive elements are avoided and, therefore, the phase shifter is capable of operation over a wide temperature range. Mechanically-delicate elements have also been avoided in the disclosed invention which, therefore, renders it capable of operation under extreme conditions of shock, vibration, pressure and acoustic noise. The invention is readily adaptable to existing balanced waveguide components, any incremental reciprocal phase shift desired can be obtained without disturbing the mechanical symmetry of the overall system packaging. Further, it is possible to incorporate the structure of the invention in existing dual waveguide structures, such as the nonreciprocal differential ferrite phase shifter circulator by telescoping the reduced-width and dielectric-loading means therein. A wide spectrum of combinations may, therefore, be realized in the practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS Details of the illustrative embodiments will be readily understood after consideration of the following detailed description and reference to the accompanying drawings, wherein:

FIG. 1 is an exploded isometric view of a balanced waveguide microwave transmission system with the illustrative embodiment of the invention shown enlarged and partially in cross section;

FIG. 2 is a cross-sectional view of an alternative embodiment of the invention;

FIGS. 3A and 3B are diagrammatic representations of non-reciprocal differential ferrite phase shift circulators utilized as isolators or duplexers in prior art balanced systems;

FIGS. 4A and 4B are diagrammatic representations of a balanced system shown in FIGS. 3A and 3B utilizing the embodiment of the invention;

FIG. 5 is a diagrammatic representation of a prior art balanced microwave duplexer system utilizing TR gas switching devices;

FIG. 6 is a diagrammatic representation of the balanced microwave duplexer system shown in FIG. 5 utilizing an embodiment of the invention;

FIG. 7 is a diagrammatic representation of the balanced microwave duplexer system shown in FIG. 5 utilizing an alternative embodiment of the invention;

FIG. 8 is a diagrammatic representation of the balanced microwave duplexer system shown in FIG. 5 with still another alternative embodiment of the invention;

FIG. 9A is a diagrammatic representation of a prior art balanced system of the folded trombone type to provide a desired additional reciprocal phase shift;

FIG. 9B is a diagrammatic representation of only a dielectric-loading waveguide section;

FIG. 9C is a diagrammatic representation of only a reduced-width waveguide section;

FIG. 9D is a diagrammatic representation of the combined balanced reciprocal microwave phase shifter of the invention shown in FIG. 1; and

FIG. 10 is a graph of the characteristic for the structures shown diagrammatically in FIGS. 9A, 9B, 9C, and

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. I, an exemplary balanced multiport nonreciprocal differential ferrite phase-shift circulator type duplexer system is shown with the individual waveguide components shown separated. The illustrative embodiment of the invention 62 providing illustratively a 90 phase shift increment is shown enlarged with the dashed lines 64 orienting the positioning in the system. In accordance with the prior art, a four-port high power duplexer comprises, at one end, a foldedtype magic-T hybrid 66 having ports 68 and 70. H- plane port 68 is coupled to the transmitter while E- plane port 70 is coupled, either, to the receiver in the ease of a duplexer, or the high power termination load in the isolator embodiment. Non-reciprocal differential phase-shifter circulator 72 comprises abutting waveguide sections 74 and 76 with ferrite bodies 77 and 78 in waveguide section 74 and ferrite bodies 79 and 80 in waveguide section 76. Ferrite bodies 77-80 are magnetized by permanent magnets 82 and 84 with the directions of polarization being opposite in adjacent waveguide sections.

The opposing end of the phase-shift circulator is connected to magic-T 86 having output ports 88 and 90. Typically, in a duplexer port 90 is coupled to a termination load while port 88 is coupled to the antenna of the system. In balanced system operation the energy coupled through port 68 is launched at port 88 while returning energy received by the antenna at port 88 emerges at port 70 to the receiver. Any uncoupled energy is absorbed by a load at port 90. Further explanation of the operation of the circulatory type balanced duplexer is schematically illustrated and described in reference to FIG. 3B.

In accordance with the invention it is now possible to add any desired reciprocal phase shift in a balanced system by the addition of dual waveguide phase shifter 62 comprising juxtapositioned waveguide sections 92 and 94 of substantially similar length. First waveguide 92 incorporates a conductive plate member 96 abutting sidewall 92a to yeild a reduced-width path for the propagation of microwaves. Second waveguide 94 is provided with a dielectric body 98, such as, for example, a body of aluminum oxide spaced from the sidewall 94a a distance z. The conductive member 96 provides for a decrease in the phase length while the guide wavelength is increased. Oppositely, however, dielectric body 98 provides for a reduction in the guide wavelength while the phase length is increased. The required dielectric loadiing is achieved in a typical application with a dielectric body 98 having shorter overall length waveguide section. The calculated results for the S- band frequency range, illustratively, 2.5 to 4.0 GHz, required a conductive plate member 96 of approximately 9.8 inches in length and width of 0.227 inches for WR 284 guide. Adjacent waveguide was dielectric-loaded by means of, illustratively, aluminum oxide body 98 having an overall length of approximately 4.4 inches, a height (x) of 0.300 inches and width (y) of 0.330 inches. The spacing (z) was approximately 0.600 inches.

In FIG. 2 another illustrative embodiment of the invention is disclosed involving the concept of telescoping the waveguide transmission components shown separately in FIG. 1. The structure shown includes dual waveguide sections 100, 100 loaded with the elongated ferrite bodies 102-105 disposed against the inside of opposing broad walls. Opposite magnetic fields are provided by permanent magnets 106 and 108 with the polar designation as shown. Similar waveguide section 100 has similar components as those just described and have been designated by a after each numeral.

The invention components to yield the desired reciprocal phase shift similar to plate member 96 and dielectric body 98 of the dual structure 62 are now incorporated directly in dual nonreciprocal phase shifters 100 and 100 to provide the increment in electrical length without disturbing the mechanical symmetry of the overall system package. The final structure is similar to that realized by telescoping the described components. A metallic plate member 112 provides the reduced-width section 100 and dielectric body 114 is disposed within the waveguide section 100. The telescoped components provide a unique waveguide transmission structure.

Referring now to FIGS. 9B-9D inclusive and FIG. 10 the performance characteristics and details of the disclosed structure will be discussed. FIG. 98 illustrates, schematically, a dual waveguide structure 116 having only dielectric means comprising a body 1 18 of a material such as aluminum oxide to load the particular waveguide section for an incremental phase shift, illustratively, 90. The body 118 has the same dimensions for height and width enumerated in connection with FIG. 1, namely, 0.330 X 0.300 inches and was spaced 1.000 from the sidewall.

Referring to FIG. 10 measurements over an operating range of, approximately 2.5 to 4.0 GHZ which is the range of the waveguide WR 284 under consideration are plotted for isolation response. The configuration of the prior art structure of the folded trombone type illustrated in FIG. 9A having one section longer than the other provides an isolation loss characterized by a single peak near the center of the band as indicated by curve A. This configuration is useful and practical over only 14 percent of the frequency bandwidth. The isolation response for the configuration shown in FIG. 98 with only the dielectric-loading on one side is indicated by the curve B in FIG. 10. Again, the performance is characterized by a single peak and the useful range with this embodiment is only 9 percent.

FIG. 9C illustrates a dual waveguide structure 116 having a conductive plate member 120 extending over substantially overall length in only one waveguide section. The conductive plate member alone provides for reduced-width of the waveguide and requires a length of approximately 13.5 inches and a thickness of 0.227 inches to yield the desired phase shift with the results shown as curve C in FIG. 10. The reduced-width section provides for a decrease in phase length while the guide wavelength is increased with a single isolation peak and useful range of 10 percent.

In FIG. 9D the dual waveguide structure includes both of the aforementioned structures shown in 9B and 9C, namely, the dielectric body 118 and conductive plate member 120 in adjacent waveguide sections. In the embodiment for propagation in WR 284 guide over the aforementioned guide operating band, dielectric body 1 18 had the same dimensions for height and width discussed in relation to FIG. 9B. The length, however, was now reduced to 4.4 inches and spaced 0.600 inches from the sidewall. The section having the conductive plate member 120 had a resultant width of 2.613 inches with a 0.227 inches thickness while the dielectricloaded section had a width of 2.840 inches. The total length of the dual structure was reduced to approximately 9.8 inches to provide the 90 reciprocal phase shift. The isolation response results are plotted in FIG. 10 as curve D. It will be noted that in place of the single peak response for the previous embodiments a two peak isolation response is noted with cross-over points on the 20 db bandwidth line approximately 39 percent apart. It is, therefore, possible to provide high power phase shifter in balanced transmission systems over a braod frequency range.

Referring now to FIGS. 4A and 4B the balanced system combinations attainable with the addition of the reciprocal phase shifter of the present invention will be discussed. In FIG. 4A the addition of a reciprocal phase shifter 122, of, illustratively, 90, introduces a new phase difference in the overall microwave system. A dual ferrite phase shifter 38, 40 is coupled to ports 1 and 3 of magic-T hybrid 32. The addition of the reciprocal phase shifter 122 permits use of two magic-T hybrids with the additional one 124 disposed at the output end coupled to ports 2 and 4 to provide a symmetrical system with the input and output E and H ports identically aligned for ease in coupling components to the system. Another combination attainable with the teaching of the invention is shown in FIG. 4B wherein magic-T 32 is now replaced with a short slot hybrid 126 providing ports 1 and 3 and an identical system at the output end with a similar hybrid 42 coupled to ports 2 and 4.

Turning next to the TR gas switching or active systems described in FIG. 5, FIG. 6 indicates that the addition of reciprocal phase shifter 122 in accordance with the invention provides in addition 90 of phase shift to provide for a split received signal with two equiamplitude, anti-phase outputs, coupled to two receivers 128 and 130. In FIG. 7, the embodiment 132 of the invention provides a reciprocal phase shifter in the duplexer which thereby transfers the entire received signal from the antenna 16 to an adjacent port, thereby reversing the position of the ports in the duplexer shown in FIG. 5. The configuration of the invention shown in FIG. 8 indicates that the addition of a 90 phase shifter 122 in the TR balanced duplexer system also permits the substitution of magic-T 134 at the output end and removal of previous hybrid 26 with ports 136 and 138 coupled respectively, to receiver 28 and in the broadest aspects. load 30. I claim:

There is thus disclosed a unique and novel structure 1 A dual balanced reciprocal waveguide phase for the addition of any desired incremental step in the Shifter Comprising; electrical length for any desired phase shift value and juxtapcsitioned rectangular waveguide Sections.

lann. w lexer Operatlon P a leclpfoca m H Ne f a dielectric body spaced from a sidewall of one of lator combinations in balanced waveguide transmission said sections and extending over a portion of its systems, including the active gas switching type and Overall g and passive ferrite circulator types are possible, without materially disturbing the symmetry of the system pack- 0 a Conductwe plate memPer for reduc mg the of the companion section contacting a sidewall aging. In view of numerous modifications, alterations I, and variations which will become evident to those thereof and extendmg substantlally throughout Its skilled in the art, it is intended that the foregoing deoverall length.

scription of the illustrative embodiments be considered 

1. A dual balanced reciprocal waveguide phase shifter comprising: juxtapositioned rectangular waveguide sections; a dielectric body spaced from a sidewall of one of said sections and extending over a portion of its overall length; and a coNductive plate member for reducing the width of the companion section contacting a sidewall thereof and extending substantially throughout its overall length. 